Degenerative loss of the nigro-striatal dopamine (DA) pathway results in deficits of sensorimotor, cognitive, and memory functions. The proposed study is designed to enhance our understanding of the roles of DA in the control of activities of striatal neurons. The study will be conducted on the rat. Some rats will receive a chemical lesion of the nigro- striatal DA pathway (i.e., an animal model of Parkinson's disease) and others will receive a lesion of the DA pathway and a subsequent graft of DA neurons (movement abnormalities are restored in these animals). The overall goals of this proposal are to determine effects of DA on electrical and pharmacological properties of the striatal neurons and to evaluate electrical and pharmacological properties of the striatal neurons that were altered after lesion of the nigro-striatal DA projections. General methods that will be used in this study include current clamp and single electrode voltage clamp recording. Intracellular labeling and retrograde labeling will be performed in order to identify the types of recorded neurons. This study is essential to the understanding of the functions of DA in the striatum. Results will shed light on the etiology of the basal ganglia disorder Parkinson's disease and may also provide information necessary for the development of more effective treatments of this disorder.